The present invention relates to flame retardant aromatic polycarbonates resulting from the blending into polycarbonate of certain arylene silicon materials having silicon atoms attached to the arylene nucleus by carbon-silicon bonds.
Prior to the present invention, certain organosilicon materials, such as organosilanes, were employed as plasticizers with polycarbonates as shown by Mark et al., U.S. Pat. No. 4,230,611. In addition, U.S. Pat. No. 4,273,691, Acquiri et al. and U.S. Pat. No. 4,387,176, Frye teach that certain silicone materials or silicone blends, when used in combination with alkaline earth metal salts, can impart improved flame retardant properties to various organic polymers.
Other flame retardants which have been employed in aromatic polycarbonates are, for example, metal salts of monomeric or polymeric-substituted aromatic sulfonic acids, such as shown by Mark et al., U.S. Pat. No. 3,933,734 and Mark, U.S. Pat. No. 3,940,366. Additional flame retardants which have been employed in aromatic polycarbonates are, for example, brominated phenyl ethers and metallic salts, such as antimony trioxide. Experience has shown, however, that although improved flame resistance has been imparted to aromatic polycarbonates utilizing the aforementioned flame retardants, undesirable toxic by-products of combustion often are emitted which have interfered with the commercial acceptance of flame retardant polycarbonates in many instances.
The present invention is based on the discovery that certain poly(arylene silicon) materials or arylene silicon polymers having chemically combined units selected from the class consisting of ##STR1## and mixtures thereof, can be incorporated into aromatic polycarbonates to impart improved flame retardant properties thereto, where a is a whole number equal to 0 or 1 and the unsatisfied valence bonds of the silicon atoms of formulas (1-3) can be satisfied by C.sub.(1-13) monovalent organic radicals, oxygen atoms or mixtures thereof.
As used hereinafter, the term "flame retardance" or "nonflammable" with respect to the flame retardant polycarbonate compositions of the present invention means that the flame retardant polycarbonates have satisfied UL94 V-O requirements for flammability, as shown by the "Flammability of Plastic Materials Bulletin" of Jan. 24, 1980. More particularly, a 5".times.1/2".times.1/8" polycarbonate test bar containing an effective amount, as defined hereinafter, of the arylene silicon material of the present invention, as shown by formulas (1-3), is suspended vertically over a 3/4 Bunsen Burner flame as provided in the aforementioned UL94 test. The test sample preferably exhibits a UL94 V-O rating which includes the following criteria:
A. Not have any specimen which burn with flaming combustion for more than 10 seconds after application of the test flame. PA1 B. Not have a total flaming combustion time exceeding 50 seconds for 10 flame applications for each set of five specimens. PA1 C. Not have any specimens which burn with flaming or glowing combustion up to the holding clamp. PA1 D. Not have any specimens which drip flaming particles that ignite dry absorbent surgical cotton located 12 inches (305 mm) below the test specimen. PA1 E. Not have any specimens with glowing combustion which persists for more than 30 seconds after the second removal of the test flame.